target/riscv: Add vstimecmp support

vstimecmp CSR allows the guest OS or to program the next guest timer
interrupt directly. Thus, hypervisor no longer need to inject the
timer interrupt to the guest if vstimecmp is used. This was ratified
as a part of the Sstc extension.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Message-Id: <20220824221357.41070-4-atishp@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/cpu.h

@@ -311,6 +311,8 @@ struct CPUArchState {
     /* Sstc CSRs */
     uint64_t stimecmp;
 
+    uint64_t vstimecmp;
+
     /* physical memory protection */
     pmp_table_t pmp_state;
     target_ulong mseccfg;
@@ -365,6 +367,8 @@ struct CPUArchState {
 
     /* Fields from here on are preserved across CPU reset. */
     QEMUTimer *stimer; /* Internal timer for S-mode interrupt */
+    QEMUTimer *vstimer; /* Internal timer for VS-mode interrupt */
+    bool vstime_irq;
 
     hwaddr kernel_addr;
     hwaddr fdt_addr;

target/riscv/cpu_bits.h

@@ -257,6 +257,10 @@
 #define CSR_VSIP            0x244
 #define CSR_VSATP           0x280
 
+/* Sstc virtual CSRs */
+#define CSR_VSTIMECMP       0x24D
+#define CSR_VSTIMECMPH      0x25D
+
 #define CSR_MTINST          0x34a
 #define CSR_MTVAL2          0x34b
 

target/riscv/cpu_helper.c

@@ -346,8 +346,9 @@ uint64_t riscv_cpu_all_pending(CPURISCVState *env)
 {
     uint32_t gein = get_field(env->hstatus, HSTATUS_VGEIN);
     uint64_t vsgein = (env->hgeip & (1ULL << gein)) ? MIP_VSEIP : 0;
+    uint64_t vstip = (env->vstime_irq) ? MIP_VSTIP : 0;
 
-    return (env->mip | vsgein) & env->mie;
+    return (env->mip | vsgein | vstip) & env->mie;
 }
 
 int riscv_cpu_mirq_pending(CPURISCVState *env)
@@ -606,7 +607,7 @@ uint64_t riscv_cpu_update_mip(RISCVCPU *cpu, uint64_t mask, uint64_t value)
 {
     CPURISCVState *env = &cpu->env;
     CPUState *cs = CPU(cpu);
-    uint64_t gein, vsgein = 0, old = env->mip;
+    uint64_t gein, vsgein = 0, vstip = 0, old = env->mip;
     bool locked = false;
 
     if (riscv_cpu_virt_enabled(env)) {
@@ -614,6 +615,10 @@ uint64_t riscv_cpu_update_mip(RISCVCPU *cpu, uint64_t mask, uint64_t value)
         vsgein = (env->hgeip & (1ULL << gein)) ? MIP_VSEIP : 0;
     }
 
+    /* No need to update mip for VSTIP */
+    mask = ((mask == MIP_VSTIP) && env->vstime_irq) ? 0 : mask;
+    vstip = env->vstime_irq ? MIP_VSTIP : 0;
+
     if (!qemu_mutex_iothread_locked()) {
         locked = true;
         qemu_mutex_lock_iothread();
@@ -621,7 +626,7 @@ uint64_t riscv_cpu_update_mip(RISCVCPU *cpu, uint64_t mask, uint64_t value)
 
     env->mip = (env->mip & ~mask) | (value & mask);
 
-    if (env->mip | vsgein) {
+    if (env->mip | vsgein | vstip) {
         cpu_interrupt(cs, CPU_INTERRUPT_HARD);
     } else {
         cpu_reset_interrupt(cs, CPU_INTERRUPT_HARD);

target/riscv/csr.c

@@ -820,6 +820,7 @@ static RISCVException sstc(CPURISCVState *env, int csrno)
 {
     CPUState *cs = env_cpu(env);
     RISCVCPU *cpu = RISCV_CPU(cs);
+    bool hmode_check = false;
 
     if (!cpu->cfg.ext_sstc || !env->rdtime_fn) {
         return RISCV_EXCP_ILLEGAL_INST;
@@ -838,7 +839,18 @@ static RISCVException sstc(CPURISCVState *env, int csrno)
         return RISCV_EXCP_ILLEGAL_INST;
     }
 
-    return smode(env, csrno);
+    if (riscv_cpu_virt_enabled(env)) {
+        if (!(get_field(env->hcounteren, COUNTEREN_TM) &
+              get_field(env->henvcfg, HENVCFG_STCE))) {
+            return RISCV_EXCP_VIRT_INSTRUCTION_FAULT;
+        }
+    }
+
+    if ((csrno == CSR_VSTIMECMP) || (csrno == CSR_VSTIMECMPH)) {
+        hmode_check = true;
+    }
+
+    return hmode_check ? hmode(env, csrno) : smode(env, csrno);
 }
 
 static RISCVException sstc_32(CPURISCVState *env, int csrno)
@@ -850,17 +862,72 @@ static RISCVException sstc_32(CPURISCVState *env, int csrno)
     return sstc(env, csrno);
 }
 
+static RISCVException read_vstimecmp(CPURISCVState *env, int csrno,
+                                    target_ulong *val)
+{
+    *val = env->vstimecmp;
+
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException read_vstimecmph(CPURISCVState *env, int csrno,
+                                    target_ulong *val)
+{
+    *val = env->vstimecmp >> 32;
+
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException write_vstimecmp(CPURISCVState *env, int csrno,
+                                    target_ulong val)
+{
+    RISCVCPU *cpu = env_archcpu(env);
+
+    if (riscv_cpu_mxl(env) == MXL_RV32) {
+        env->vstimecmp = deposit64(env->vstimecmp, 0, 32, (uint64_t)val);
+    } else {
+        env->vstimecmp = val;
+    }
+
+    riscv_timer_write_timecmp(cpu, env->vstimer, env->vstimecmp,
+                              env->htimedelta, MIP_VSTIP);
+
+    return RISCV_EXCP_NONE;
+}
+
+static RISCVException write_vstimecmph(CPURISCVState *env, int csrno,
+                                    target_ulong val)
+{
+    RISCVCPU *cpu = env_archcpu(env);
+
+    env->vstimecmp = deposit64(env->vstimecmp, 32, 32, (uint64_t)val);
+    riscv_timer_write_timecmp(cpu, env->vstimer, env->vstimecmp,
+                              env->htimedelta, MIP_VSTIP);
+
+    return RISCV_EXCP_NONE;
+}
+
 static RISCVException read_stimecmp(CPURISCVState *env, int csrno,
                                     target_ulong *val)
 {
-    *val = env->stimecmp;
+    if (riscv_cpu_virt_enabled(env)) {
+        *val = env->vstimecmp;
+    } else {
+        *val = env->stimecmp;
+    }
+
     return RISCV_EXCP_NONE;
 }
 
 static RISCVException read_stimecmph(CPURISCVState *env, int csrno,
                                     target_ulong *val)
 {
-    *val = env->stimecmp >> 32;
+    if (riscv_cpu_virt_enabled(env)) {
+        *val = env->vstimecmp >> 32;
+    } else {
+        *val = env->stimecmp >> 32;
+    }
+
     return RISCV_EXCP_NONE;
 }
 
@@ -869,6 +936,10 @@ static RISCVException write_stimecmp(CPURISCVState *env, int csrno,
 {
     RISCVCPU *cpu = env_archcpu(env);
 
+    if (riscv_cpu_virt_enabled(env)) {
+        return write_vstimecmp(env, csrno, val);
+    }
+
     if (riscv_cpu_mxl(env) == MXL_RV32) {
         env->stimecmp = deposit64(env->stimecmp, 0, 32, (uint64_t)val);
     } else {
@@ -885,6 +956,10 @@ static RISCVException write_stimecmph(CPURISCVState *env, int csrno,
 {
     RISCVCPU *cpu = env_archcpu(env);
 
+    if (riscv_cpu_virt_enabled(env)) {
+        return write_vstimecmph(env, csrno, val);
+    }
+
     env->stimecmp = deposit64(env->stimecmp, 32, 32, (uint64_t)val);
     riscv_timer_write_timecmp(cpu, env->stimer, env->stimecmp, 0, MIP_STIP);
 
@@ -1814,6 +1889,7 @@ static RISCVException rmw_mip64(CPURISCVState *env, int csrno,
     if (csrno != CSR_HVIP) {
         gin = get_field(env->hstatus, HSTATUS_VGEIN);
         old_mip |= (env->hgeip & ((target_ulong)1 << gin)) ? MIP_VSEIP : 0;
+        old_mip |= env->vstime_irq ? MIP_VSTIP : 0;
     }
 
     if (ret_val) {
@@ -3680,6 +3756,12 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = {
                        .min_priv_ver = PRIV_VERSION_1_12_0 },
     [CSR_STIMECMPH] = { "stimecmph", sstc_32, read_stimecmph, write_stimecmph,
                         .min_priv_ver = PRIV_VERSION_1_12_0 },
+    [CSR_VSTIMECMP] = { "vstimecmp", sstc, read_vstimecmp,
+                        write_vstimecmp,
+                        .min_priv_ver = PRIV_VERSION_1_12_0 },
+    [CSR_VSTIMECMPH] = { "vstimecmph", sstc_32, read_vstimecmph,
+                         write_vstimecmph,
+                         .min_priv_ver = PRIV_VERSION_1_12_0 },
 
     /* Supervisor Protection and Translation */
     [CSR_SATP]     = { "satp",     smode, read_satp,     write_satp     },

target/riscv/machine.c

@@ -92,6 +92,7 @@ static const VMStateDescription vmstate_hyper = {
         VMSTATE_UINTTL(env.hgeie, RISCVCPU),
         VMSTATE_UINTTL(env.hgeip, RISCVCPU),
         VMSTATE_UINT64(env.htimedelta, RISCVCPU),
+        VMSTATE_UINT64(env.vstimecmp, RISCVCPU),
 
         VMSTATE_UINTTL(env.hvictl, RISCVCPU),
         VMSTATE_UINT8_ARRAY(env.hviprio, RISCVCPU, 64),

target/riscv/time_helper.c

@@ -22,6 +22,14 @@
 #include "time_helper.h"
 #include "hw/intc/riscv_aclint.h"
 
+static void riscv_vstimer_cb(void *opaque)
+{
+    RISCVCPU *cpu = opaque;
+    CPURISCVState *env = &cpu->env;
+    env->vstime_irq = 1;
+    riscv_cpu_update_mip(cpu, MIP_VSTIP, BOOL_TO_MASK(1));
+}
+
 static void riscv_stimer_cb(void *opaque)
 {
     RISCVCPU *cpu = opaque;
@@ -47,10 +55,16 @@ void riscv_timer_write_timecmp(RISCVCPU *cpu, QEMUTimer *timer,
          * If we're setting an stimecmp value in the "past",
          * immediately raise the timer interrupt
          */
+        if (timer_irq == MIP_VSTIP) {
+            env->vstime_irq = 1;
+        }
         riscv_cpu_update_mip(cpu, timer_irq, BOOL_TO_MASK(1));
         return;
     }
 
+    if (timer_irq == MIP_VSTIP) {
+        env->vstime_irq = 0;
+    }
     /* Clear the [V]STIP bit in mip */
     riscv_cpu_update_mip(cpu, timer_irq, BOOL_TO_MASK(0));
 
@@ -95,4 +109,6 @@ void riscv_timer_init(RISCVCPU *cpu)
     env->stimer = timer_new_ns(QEMU_CLOCK_VIRTUAL, &riscv_stimer_cb, cpu);
     env->stimecmp = 0;
 
+    env->vstimer = timer_new_ns(QEMU_CLOCK_VIRTUAL, &riscv_vstimer_cb, cpu);
+    env->vstimecmp = 0;
 }